How to display customers that have not bought an item in a pivot report

my aim was for them to just enter the product code in a field and for the formula to return the customer list for those customers with no sales for that product.

not sure if i can do with a formula - but can have ago
if its an extraction , I have done something like that for a warranty report -

so if they just add the product - do they also add a date range or is it just previous month
so now it would show FEB
then when MAR is loaded , just show MAR

Who does the loading of the data and updating the pivot tables (refresh ) etc ?

can you load a sample of real data and how structured - with dummy info in
customer ID
Products codes etc

then we have something to work on thats close to real , rather than your example and then need to change all the formulas for a real database structure